Apparatus for production of tubular blown foils of polyvinyl chloride interpolymers



3,044,1 l4 FOILS 0F July 17, 1962 E. PIROT APPARATUS FOR PRODUCTION OFTUBULAR BLOWN POLYVINYL CHLORIDE INTERPOLYMERS Original Filed Feb. 21,1953 .il.. ll..l .il nufli \QI ATT'YS United States Patent 3,044,114APPARATUS FOR PRODUCTIGN 0F TUBULAR BL'OWN FUELS 0F P01. 1 I

CHLOE INTERPOLYNIERS Ernst Pirot, Wuppertal-Barmen, Germany, assignor toJ. P. Bemberg Airtiengesellschaft, Vtuppertai-Oberbarmen, GermanyOriginal application Feb. 21, 1958, Ser. No. 716,634, new Patent No.3,009,208, dated Nov. 21, 1961. Divided and this application Dec. 22,1958, Ser. No. 782,132 Claims priority, application Germany Mar. 2, 19574 Claims. (Cl. 18-14) This invention relates to apparatus for theproduction of tubular foils of polyvinyl chloride interpolymers whereindecomposition, due to excessive temperatures heretofore essential to theoperation, may be avoided. This application is a divisional applicationof my copending application Serial No. 716,634, filed February 21, 1958,now Patent No. 3,009,208.

More particularly, this invention relates to apparatus for theproduction of tubular foils of polyvinyl chloride and interpolymers ofpolyvinyl chloride of substantially transparent nature, free from odorand color-producing decomposition products, particularly suited for usein packaging and transportation of foodstuffs.

Heretoiore, foils and tubes of polyvinyl chloride and interpolymers ofpolyvinyl chloride have been produced by means of rollers as is commonin calendering processes. Usually the procedure is carried forward byconducting either a cast foil from a solution or a previously calenderedsheet of interpolymer over heated rollers under pressure whereby thefoil is reduced in thickness and increased in dimension until of theappropriate thickness for its ultimate use. Heretofore in processing, asdescribed above, emulsions have been used containing alcohols, oils,waxes and resins homogeneously dispersed and distributed in theinterpolymers.

In the prior art processing of interpolymers of polyvinyl chloride,serious limitations have been faced due to the tendency of hydrogenchloride to be liberated from the interpolymers which, under the usualconditions of processing, cannot escape and causes an autocatalyticdecomposition reaction in the polymeric material. Hydrogen chlorideliberation and decomposition of polyvinyl chloride polymers takes placerapidly at temperatures especially from about 180 C. upwards. As thetemperature is increased the rate of decomposition is also increased.Thus, a serious limitation is met in the amount of heat which may beused in forming films and foils of polyvinyl chloride and polyvinylchloride containing interpolymers.

It is known that decomposition due to release of autocatalytic hydrogenchloride can be controlled in part and prevented in part by compoundingthe above class of interpolyrners with known stabilizers. Thesestabilizers in general operate by reacting with or otherwise removingfrom immediate contact with the polymer the hydrogen chloride as it isreleased. Many stabilizers are already known and new stabilizers arebeing constantly introduced. Among those in use are, for example, anumber of organic tin compounds, illustratively, dibutyl tin dilaurate,calcium ricinoleate, phenylindol, and other hydrogen chloride acceptorsboth of organic and inorganic nature. Despite a relative value-of thesematerials to prevent the development of discoloration in films andfoils, they are not altogether successful and even when presentinformation of polyvinyl chloride films and foils at temperaturesessential to malaxation, extrusion and blowing, objectionabledecomposition takes place.

Blown foils are obtained which fail to meet requirements for commercialacceptance, particularly in the all) packaging of foodstufis. Blownfoils produced by prior art processes must be able to withstandrelatively high temperatures of the order of 190 C. to 210 C. in orderthat the mass may be handled during the blowing or tubular film-formingstep.

Still another disadvantage of attempting to form tubular films ofpolyvinyl chloride by the prior art processes lies in the fact thatprior art equipment can be operated only a brief period of time beforethe products of par tial decomposition clog and render the apparatususeless. Generally the prior art apparatus becomes so fouled that itmust be subjected to cleaning after periodic use of the order of 8-10hours.

A further limitation upon the prior art method of forming tubes ofpolyvinyl chloride is that polymers having a K-value only up to about 60can be used. As the K-value has relation to the molecular Weight ofthe'polymer, it is a limitation upon the quality of polymer which may beemployed for packaging purposes. If one attempts to utilizeinterpolymers of polyvinyl chloride having K-values of the order of 70,the difficulties of processing through heating and calendering aspresently practiced with lower molecular weight materials aremultiplied. On the other hand, higher molecular weight materials areparticularly desired for use in tubes and foils because they are morefree from odor and tastes which may be transferred to delicatefoodstuffs.

In the method described in my said copending application Serial No.716,634, polyvinyl chloride interpolymers are combined with a particularclass of volatile organic solvents which do not belong to any particularchemical class of compositions but which are definable in relation totheir physical specifications.

The useful volatile organic solvents are limited to those which have aboiling point between about C. and about 210 C. which, at normal or roomtemperatures (25 C.) are nonsolvents for polyvinyl chlorideinterpoiymers but act as diluents for said interpolymers when insolution at room temperature. These diluents or nonsolvents forpolyvinyl chloride interpolymers at room temperature will, however, whenheated with the polymers at temperatures above 100 C. exert solventaction causing the polymeric substances to become somewhat gelatinous innature and of decreased shear resistance despite the fact that theK-values thereof may be in excess of 60 and of the order of 70.

The volatile organic solvents which serve as diluents at roomtemperature and solvents at temperatures above 100 C. include a widevariety of volatile organic solvents. Among the illustrative classes arealiphatic ethers, aliphatic esters, volatile aromatic hydrocarboncompounds, cycloaliphatic compounds, substituted aromatic andcycloaliphatic compounds particularly those containing halogensubstituents, etc. Additionally and specifically illustrative aredipropyl ether, dibutyl ether, the higher dialkyl ether homologues,glycol monoethyl ether, glycol monopropyl ether, glycol monoacetate,glycol diacetate, glycol monopropionate, glycol dipropionate; the wellknown mixed esters illustrative of which are glycol monoacetatemonopropionate, glycol monopropionate monobutyrate, etc. Illustrative ofthe aromatic compounds are toluene, Xylene and the halogen substitutedaromatic compounds including monochloro-benzene, monochlorotoluene,dichlorotoluene, etc. Multiple ring aromatic compounds which are usefulinclude as illustrative, tetrahydro naphthalene, decahydro-n'aphthaleue,etc. Still other compounds are useful as will be apparent from theforegoing exemplary compounds which suggest others from which groups oneskilled in the art may select many other species than those specificallyset out herein.

In the method of malaxation and extrusion, the polyvinyl chlorideinterpolymers, illustratively, 100 parts by amt-rare weight of the same,are thoroughly intermixed with from to 25 parts by weight of thevolatile organic hereafter in greater detail. In this apparatus theprocess of intermixing of the volatile organic solvent, polyvinylchloride interpolymer, and preferably a stabilizer, is subjected tomalaxation and extrusion steps as the temperature is slowly increasedfrom room temperature to not above about 180 C. and more particularlyfrom 100 C. to 180 C. under carefully controlled increment increase intemperature between the limits indicated. By thus slowly intermixing,malaxation and extrusion under anaerobic environment in an atmospheresurrounded by a diluent vapor, the polyvinyl chloride interpolymer isprogressively changed from a heterogeneous mixture of diluent andpolymer as the temperature is increased to a more and more homogeneousgelatinous product.

At the upper limit of temperature but not above about 180 C., thegelatinous material may be extruded in the form of a strand. It maythereafter be reduced in length and is in a condition to be transferredto a second opera- ;tion whereupon a blowing mechanism, as known in theart, acts to transform the physical nature of the processedinter-polymer into tubes, foils, etc. Forming in' this man? nor couldnot be accomplished heretofore with polymers having a K-value of theorder of 60 and above without decomposition. The decomposition informing is sutficientto render the ultimate foil unsuited for commercialapplication and particularly for use in food packaging. Preferably,however, the blowing mechanism for the formation of the foil followsdirectly and immediately subsequent to the described method ofpreparation of homogeneous'gelatinous polyvinyl chloride interpolyrnersfor extrusion. 7

As blowing mechanisms are well known and not, of themselves, a part ofthis invention, detailed description thereof is not essential to thepresent invention in apparatus and process.

The term polyvinyl chloride interpolymers as used herein is intended toinclude interpolymers containing a major percentage of vinyl chloride,for example, the percentage of vinyl chloride may be varied from 100% toabout 85% with at most of a second polymerizable monomer compoundinterpolymerized therewith. Interpolymers'of polyvinyl chloride are wellknown in the art 'and include, as illustrative of the minor component,

particular to the drawings, a first entry chamber 1 is mounted above asecond elongated central chamber 21 which, in a preferred form of theinvention, feeds to an extrusion orifice 37' leading into a blastinghead 10. A central shaft 23 is deeply threaded along the greater part ofits length with helical threads 24. Shaft 23 is mounted centrally withinthe entry chamber 1 and the elongated central chamber 21. Raw material,including polyvinyl '7 chloride interpolymer, stabilizer and solvent, isfed through inlet means 16 into the receiving vessel 2 having controlvalve 25 making it possible to seal the interior of chambers l and 21 toprovide an anaerobic atmosphere saturated with the selecteddiluent-solvent. A 'heat exchanger 27, containing heat exchange coil 15for condensing vapors of said diluent-solvent, is also controlled bymeans of valve 28 (and other valves not shown) so that the apparatus maybe operated under pressures increased or diminished over normalatmospheric pressure, or may be operated at atmospheric pressuredepending upon the nature of the solvent-diluent selected for use in themethod. A second screw 30 axially parallel to shaft 23 and inapproximate contact at its outer periphery with screw 24 is adaptedatorotate in an opposite direction to shaft 23 thereby kneading andforcibly directing material fed to the upperfchamber 1 downwardlythrough chamber 21 by the positive screw feed resulting from therotation of shaft 23, urging the mix downward by means of the action ofhelical screws 24 and 4.

Temperature control within the elongated central chamber 21 ismaintained by a plurality of heat exchangers 9, 8, 7, 6 and 5 mountedinseries along its length and about its periphery having ingress 35 andegress means 37 for pumping into and through each of said units a heatexchange fluid.

In one modification of the invention, the hot heat exchange fiuid may beforced into the bottom entry 35 of heat exchanger 9 and thence upwardcountercurrently to the flow of material downwardly through theelongated central chamber 21, in sequence through heat exchangers 9, 8,7, 6, 5 and thus to discharge through the exit tube 37 of heat exchanger5. Again alternatively, each of the heat exchangers s, 6, 7, 8 and 9 maybe electrically heated and controlled by automatic or manual meanswithin a pre-set temperature range limit.

For example, in one use and application of the apparatus, heat exchanger5 is held bet-ween and C., heat exchanger 6 at C., heat exchanger 7 atC., number 8 at C., and number 9 heat exchanger between and C. The upperentry chamber 1 may also be provided with agitator units 14 which assistin intermingling of the interpolymer, stabilizers volatile organicdiluents therefor, etc. The organic diluent can, if desired, be meteredinto the chamber by a metering pump through orifice 36.

As the interpolymer and diluent are intensively intermixed, kneaded andforced downwardly through elongated tube 21, past zones of increasingtemperature, the intermixture begins to gelatinize slowly as theinactive diluent transforms to an active solvent for the interpoly meras the temperature of the diluent is increased. Be fore entry into theblasting head 10 the malaxated gelatinized mixture is forced through theorifice 37' and may be collected at this point as an extruded strand tobe reduced in length for further processing.

Preferably, however, blasting head '10 is immediately adjacent andfollowing orifice 37' and the gelatinized interpolymer directlysubjected to blowing by extrusion about mantle 38 and between it and theorifice 39. Gases may be passed in at 19 andthrough element 18interiorly of the tube and out through opening 41 and pipe '42, v whileother gases are passed through orifices 17 and about the exterior of thetube and out at 19a to provide control of the forming tube of polyvinylchloride at this point. As the formed tubular foil passes out at 13through orifice 40, the diameter controlling and calibrating mantle. 12held at a temperature of 7075 C. assists in control of the thickness ofand the diameter of the tube so extruded.

As the formed tubular foil is removed at 13, it may thereafter passthrough a pair of squeezing rollers, a cutting device and a pair ofwinding rollers as is oftentimes use in this art. Solvent-diluent whichmay be held in the extruded tubular foil is removed at least in part bymeans of air injection at 17 and 18. 'Injectecl air may be forcedthrough the drying chamber 11 under controlled temperature to remove thesolvent present in the foil.

The K-value as referred to above is a parameter denoting the molecularsize of the polymer and has relation to the temperature at which thematerial tends to become thermoplastic as well as the viscosity ofsolutions thereof. The general range of K-value of polyvinyl chlorideinterpolymers may be as low as 10 and as high as 150 or more with valuesof 30 .to 100 more generally referred to as in the low to high range.Additional information relative to the term K-value as it applies topolymers may be found in Cellulosechemie 13, 8, 1932, by H. Fikentscher.

The invention is hereby claimed as follows:

1. Apparatus for production of a tubular foil from a polymer-solventmass comprising a closed mixing vessel, supply means communicating withsaid vessel for feeding a solid polymer to said vessel, additionalsupply means for feeding a liquid solvent into said vessel, an elongatedfirst screw with its feed end in said vessel, said first screw beingrotatably driven by a shaft extending through said vessel, an agitatormounted on said shaft and inside said vessel whereby said agitatorrotates with said first screw and shaft, an auxiliary second screwwithin said vessel and immediately adjacent to said first screw to feedsaid solid polymer and said liquid solvent into the path of rotation ofsaid first screw, a screw housing projecting from said vessel with saidfirst screw extending into said housing, heating means surrounding saidhousing, a chamber at the discharge end of said first screw andcommunicating with said housing, said chamber having an annulardischarge orifice, and means at the discharge end of said chamber forblowing the polymer-solvent mass discharged by said annular orifice intoa thin film of tubular form.

2. Apparatus for production of a tubular foil from a polymer-solventmass comprising a closed mixing vessel, supply means communicating withsaid vessel for feeding a solid polymer to said vessel, additionalsupply means for feeding a liquid solvent into said vessel, a solventvapor condenser communicating with said vessel, said condenser adaptedto condense solvent vapors and return the condensed solvent to saidvessel, an elongated first screw with its feed end in said vessel, saidfirst screw be ing rotatably driven by a shaft extending inside saidvessel whereby said agitator rotates with said first screw and shaft, anauxiliary second screw within said vessel and immediately adjacent tosaid first screw to feed said solid polymer and said liquid solvent intothe path of rotation of said first screw, a screw housing projectingfrom said vessel with said first screw extending into said housing,heating means surrounding said housing, said chamber having an annulardischarge orifice, and means at the discharge end of said chamber forblowing the polymersolvent mass discharged by said annular orifice intoa thin film of tubular form.

3. In apparatus for blowing a thermoplastic mass into a tubular foil, afoil drying chamber with an annular entrance orifice at one end thereofand a cylindrical wall orifice at the opposite end thereof, gas egresspassage means at said one end positioned eccentrically within saidannular orifice, a gas conduit concentric with said annular orifice,said egress and said conduit being jointly smaller in diameter than saidannular orifice, said conduit extending into said chamber through saidone end, said conduit terminating in said chamber and adapted to blow agas inside a tube extruded through said annular orifice and out throughsaid egress, means for circulating a gas through said chamber about theouter side of said extruded tube, and heat exchange means formaintaining said cylindrical wall at a predetermined, controlledtemperature.

4. In apparatus for production of a tubular foil, a first chamber with aforwardly directed annular orifice, a blasting head positioned centrallywithin and smaller than said annular orifice, means for forcing aplastic mass through said orifice and about said blasting head in theform of a tube, gas egress passage means extending longitudinallythrough said blasting head, gas ingress passage means extendinglongitudinally through said blasting head, a second enlarged chamberextending forwardly from said first chamber, a gas supply conduitprojecting forwardly from said blasting head concentrically within saidtube, said conduit serving as an extension of said ingress passagemeans, means for circulating gas through said enlarged chamber and aboutthe outside of said tube, a mantle with an internal cylindrical wallprojecting forwardly from said enlarged chamber opposite said annularorifice, and means to maintain said wall at a controlled, predeterminedtemperature.

FOREIGN PATENTS 986,585 France Aug. 2,

1.4. IN APPARATUS FOR PRODUCTION OF A TUBULAR FOIL, A FIRST CHAMBER WITHA FORWAEDLY DIRECTED ANNULAR ORIFICE, A BLASTING HEAD POSITIONEDCENTERALLY WITHIN AND SMALLER THAN SAID ANNULAR ORIFICE, MEANS FORFORCING A PLASTIC MASS THROUGH SAID ORIFICE AND ABOUT SAID BLASTING HEADIN THE FORM OF A TUBE, GAS EGRESS PASSAGE MEANS EXTENDING LONGITUDINALLYTHROUGH SAID BLASTING HEAD, GAS INGRESS PASSAGE MEANS EXTENDINGLONGITUDINALLY THROUGH SAID BLASTING HEAD, A SECOND ENLARGED CHAMBEREXTENDING FORWARDLY FROM SAID FIRST CHAMBER, A GAS SUPPLY CONDUITPROJECTING FORWARDLY FROM SAID BLASTING HEAD CONCENTRICALLY WITHIN SAIDTUBE, SAID CONDUIT SERVING AS AN EXTENSION OF SAID INGRASS PASSAGEMEANS, MEANS FOR CIRCULATING GAS THROUGH SAID ENLARGED CHAMBER AND ABOUTTHE OUTSIDE OF SAID TUBE, A MANTLE WITH AN INTERNAL CYLINDRICAL WALLPROJECTING FORWARDLY FROM SAID ENLARGED CHAMBER OPPOSITE SAID ANNULARORIFICE, AND MEANS TO MAINTAINN SAID WALL AT A CONTROLLED, PREDETERMINEDTEMPERATURE.